If i say that there are many far superior games to COD, and you say that the quality of COD games is undeniably high then we're saying subtly different things. There are many polished high quality games that are simply bad games. There are lists of design flaws, graphical issues, art design issues and gameplay scenario design flaws that exist in COD games. What COD games do well (i.e. the multiplayer aspect) they do exceedingly well, arguably better than most other FPS games. There are still lots of far superior games out there, with equal or superior levels of polish, equally or superior gameplay, superior level and scenario design, much better stories & voice acting, far better sound design & direction etc etc etc...
Sales are also not a sensible testament to a game's overall quality. If anything BLOPS proves my point over MW1 which was a superior game. Still, fundamentally i agree that COD games are high quality experiences, but they're not the best games ever made, there are far more better games that have been made in existence and thus i can and will happily say that there are many far superior games. You may disagree but you're entitled to your own opinion and subjective tastes ;-)